Allow upload of CA certs for self signed certificate use

[madhav165]

✨ Feature / Enhancement PR

🔗 Epic / Issue

Link to the epic or parent issue:
Closes #1278, #1287, #1364

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🚀 Summary (1-2 sentences)

Adds first-class support for self-signed TLS by allowing users to upload a custom CA certificate. The CA is wired through gateway create/update flows, health checks, and tool calls, with UI-side file validation and updated docs.

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🧪 How to Test This Feature

Quick Setup

1. Get your CA certificate file - If your MCP server uses a self-signed certificate, you'll need the CA certificate file (usually named something like cert.pem, ca.pem, ca.crt, or rootCA.pem)

2. Open the MCP Gateway Admin Panel - Navigate to your gateway instance and log in as an admin

Testing Steps

Step 1: Add a New Gateway with CA Certificate

1. Go to Admin → Gateways tab
2. Click Add Gateway
3. Fill in your server details:
   • Name: My Test Server
   • URL: https://your-mcp-server.example.com (must be HTTPS)
4. Scroll to the CA Certificate section
5. Drag your certificate file (.pem, .crt, .cer, or .cert) into the upload area, or click to browse
6. You should see a green checkmark: ✅ "All certificates validated successfully!"
7. Click Save

Step 2: Verify the Connection Works

1. After saving, the gateway should show as "Active" or "Reachable"
2. Go to the Tools tab
3. You should see tools from your newly added gateway listed
4. Try invoking one of the tools to confirm it works

Step 3: (Optional) Test Multiple Certificate Files
If you have a certificate chain (root + intermediate CAs):

1. Select multiple certificate files when uploading
2. The system will automatically order and combine them
3. You'll see each file validated individually

What You Should See

✅ Success indicators:

• Green checkmark after upload
• Gateway shows as connected/reachable
• Tools are discovered from the server
• Tool invocations work without SSL errors

❌ If something's wrong:

• Red X with error message (check file format or size)
• Gateway shows as unreachable (check URL or certificate)

Need Help?

If you encounter issues:

1. Check that your certificate file is in PEM format
2. Verify the URL matches your server's certificate CN/SAN
3. Ensure the file is under 10MB
4. See the full documentation at: docs/docs/manage/self-signed-certificates.md

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🧪 Checks

• make lint passes
• make test passes
• CHANGELOG updated (if user-facing)
• Documentation added (docs/docs/manage/self-signed-certificates.md)

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